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Fifteen Herd Health Lessons

You enter your production facilities and immediately sense that something is not right with the herd. It's quieter than normal; few animals stand. Over 10% of the animals aren't eating, even though there's ample water. Walking the barn, you note a few abortions, a slight cough. Your veterinarian inspects the animals, collects blood and tissue samples for laboratory submission, and recommends waiting

David Reeves, DVM, College of Veterinary Medicine, University of Georgia | Oct 15, 2004

You enter your production facilities and immediately sense that something is not right with the herd. It's quieter than normal; few animals stand. Over 10% of the animals aren't eating, even though there's ample water.

Walking the barn, you note a few abortions, a slight cough. Your veterinarian inspects the animals, collects blood and tissue samples for laboratory submission, and recommends waiting for the diagnosis before taking any action. He offers words of encouragement, yet you still feel a sense of desperation.

Frustration mounts with more abortions, more coughing, too many sows dying and unthrifty pigs. This scenario becomes the norm as the disease becomes endemic within the herd. Vaccine and medication costs mount.

Unfortunately, this is a frequent scenario that begs the question: “What is the best system for health maintenance for your farm or system?”

This article examines health management systems and explores disease dynamics, including predisposing conditions using a series called “lessons learned.”

Lesson #1

Health cannot be protected by one approach because one program does not fit all. Health is a complex equation that becomes even more complex when factoring in disease dynamics within populations, variations in management, individual animals and environmental effects. In basic terms, epidemiologists describe these interactions as the disease triad: host, environment and pathogen.

Described mathematically, disease in the animal is inversely proportional to animal resistance, and directly proportional to pathogen load (challenge dose) and pathogen virulence.

Likewise, health is the inverse of this equation and is easily understood at the individual animal level. But, at the herd level, disease becomes much more complex. Epidemiologists use equations to quantify how different risk factors contribute to the likelihood of disease occurrence. Contributing to disease are the animal number, infectious agent, pathogen virulence, organic matter and auxiliary host. Contributing to health are downtime, drying, temperature, pressure, light, vaccines, chemical inactivation and antimicrobials.

For example, some pathogens are very contagious (possess the capability to spread) and others are not; some are highly infectious (possess the capability to cause infection) and others are not.

Porcine reproductive and respiratory syndrome (PRRS) is not a highly contagious organism, yet it is highly infectious (a small amount of the virus can establish infection in an animal).

Because PRRS is not highly contagious, it is easy to understand why naïve animals can be present in herds, particularly large herds with high replacement rates. Because it is highly infectious, it is easy to understand why small amounts of the virus, such as those found in contaminated trucks or needles, can cause infection.

It also helps us understand why crossfostering piglets between litters enhances PRRS spread within farms, and why mixing infected and non-infected pigs at weaning has devastating consequences.

In contrast, salmonella are very contagious, yet not highly infectious. Thus, salmonella are easily spread and present on many if not most farms. Yet they infrequently cause disease because very large numbers are required for infection.

This lesson teaches that while designing a system to control one disease may be easy, designing one to address multiple agents is challenging because pathogens are not created equal. Comprehensive disease control programs must feature control measures for all pathogens and management and environmental factors.

Lesson #2

Comprehensive biosecurity systems are by nature complex, difficult to design and very hard to administer — and they are critical. One mistake on a single day by a single person can bring disaster, which is why many biosecurity systems fail. They lack focus, appear difficult and typically are not adequately explained, and therefore are not fully implemented.

To simplify matters, control measures should be segregated into those that are best controlled at the system level and those that are best controlled at the farm or local level. Both are of equal significance, yet it is important that only the daily critical elements remain at the local level. This approach removes many concerns typically controlled at the farm level.

Figure 1 is a fishbone diagram illustrating this point. Health is dependent on components that should be assigned to system level control (the top branch) and those that should be assigned to local control (the lower branch).

Systematic measures are those that should be designed and managed by someone who is not typically present on the farm every day, yet has the time and expertise to accomplish key biosecurity elements. This person focuses on the design of the health program and then monitors replacement and semen sourcing protocols, isolation and acclimation and vaccination and medication.

In contrast, local control addresses issues such as traffic control, transport sanitation, vector control and dead animal disposal. This division makes biosecurity programs less cumbersome and allows for accountability.

Lesson #3

Limit breeding stock sources. Closing herds to new animal infusions has great potential to limit disease risk. However, when impractical, limit sources to as few as possible. As the number of replacement and semen sources increases linearly, disease risks increase exponentially.

Lesson #4

Isolation and acclimation of incoming breeding stock are essential. It is common knowledge that isolation for incoming breeding stock is needed for observation and testing. Veterinarians now recognize that acclimation is also crucial to reduce the pathogen load circulating within the breeding herd. Through vaccination or exposure to pathogens, incoming replacements will hopefully become immune or minimal shedders before entering the herd. The proper time interval and best way to stimulate immunity are farm- and pathogen-dependent.

Lesson #5

Most pig diseases come from other pigs, so the first step is to limit exposure to other pigs (see Lesson #3).

Second, limit exposure to “pig elements” which can be found on the bottom of worker boots and on clothing, hands or hair. At a minimum, staff and visitors should only wear farm-provided boots and garments and wash their hands before entry. Just washing hands between rooms can impact transmission of disease within farms.

Taking this concept further, work by Sandy Amass, DVM, Purdue University, suggests that shower-in, shower-out is needed to fully prevent farm-to-farm transmission of diseases such as E. coli associated with neonatal diarrhea.

The direction of people traffic is also important. Figure 2 depicts a health pyramid. Ideally, there should be no traffic between the pyramid elements. But if necessary, flow should only be from the point of greatest potential harm to the point of least potential harm (boar stud toward finishing) and not in reverse.

The amount of downtime between units is a hotly debated subject among veterinarians. While everyone agrees that it has benefit and the interval is farm- and system-dependent, it is the interval length that is argued.

For example, 48 hours of downtime may be required to visit elements at the top of the pyramid, while little or no downtime may be required for finishing units. Obviously, variation in health status is the key determinant for site visits. No one should go from sick herds to healthy herds.

Lesson #6

Distance is often the best means of keeping disease out. One of the great failings of current production systems in the U.S. is the location of sow units close to nursery-finishing facilities. Aerosol, insect and vermin have been linked to numerous outbreaks of disease between closely located units.

For example, epidemiology models in Europe and the U.S. suggest that pseudorabies (PRV) and foot-and-mouth disease can be spread farm-to-farm by aerosol, with wind and humidity playing significant roles. It is likely that other diseases are spread by aerosol, too.

Insects can play a key role in farm-to-farm transmission of disease. This has been reinforced recently in work by Scott Dee, DVM, University of Minnesota. Insects play a role in mechanically transmitting PRRS between farms. In Dee's study, PRRS-carrying flies were found over two miles from the farm where they came in contact with infected animals. Flies can also harbor Transmissible gastroenteritis (TGE), PRV, hog cholera virus and Streptococcus suis.

Mosquitoes are also a real concern, though they harbor PRRS for less than six hours.

Lesson #7

Because disease can be easily transmitted between farms, siting becomes a vital biosecurity concern. During the 1970s and later, many production systems built facilities, including sow units, near packers without regard for disease spread.

Figure 3 depicts how the U.S. system is currently configured with sow, nursery and finisher units clustered around a packer. Many now recognize this mistake. Sow units have been repeatedly infected, even after depopulation/ repopulation, parity segregation or closed herd technologies have been applied.

The low cost of hauling young pigs to finishers in the Corn Belt from sow units on the grain belt fringe can easily offset the recurring cost of disease within sow herds.

For this reason, we propose that a more reasonable system segregates units by type of production (Figure 4).

Lesson #8

Sanitizing facilities is more dependent on cleaning, drying and downtime than is disinfection in managing total pathogen load. Although disinfecting is the most-discussed aspect of sanitation, Table 1 demonstrates that proper cleaning, drying and downtime are much more important.

This is not to diminish the importance of disinfecting, but to emphasize that front-end preparation is vital for it to be effective.

One of the most overlooked aspects of room and truck preparation is drying. The poultry industry has emphasized this point for years. Recent work by Montserrat Torremorell, DVM, of PIC suggests its importance to the swine industry. Placing sows in farrowing rooms still wet from cleaning, and loading trucks that are not dry, negates much of the work effort.

Lesson #9

Selecting the appropriate class of disinfectant is very important. This is actually an old lesson, recently reinforced.

In the past, the focus was on rotating disinfectants to keep them effective. We now know it's more important to select disinfectants based on the infectious agent to be controlled.

For instance, if PRRS is a concern, then gluteraldehyde or quaternary ammonia compounds are indicated; however, if E. coli is the target, choose a phenolic compound.

Lesson #10

Trucks are a risk factor for transmitting disease agents between farms. Truck-sanitizing protocols should be in place and executed to detail. Again, Dee has demonstrated that pathogens such as PRRS and Streptococcus suis can persist on truck tires between farms.

Table 1. Effect of Various Washing Steps

State of house

Viable bacteria/sq. cm

Immediately after pig removal

50,000,000

After plain washing

20,000,000

Hot water wash + detergent

100,000

Target before disinfection

1,000

Dee and Amass have also shown that while disinfection of truck tires is beneficial, this step alone only helps reduce tire contamination. Further, it is not a substitute for cleaning the entire vehicle, because it is not uncommon for the interior truck floor to be contaminated, as well as the wheel housing.

If a tire sanitizer is used, its efficacy is highly dependent on environmental conditions.

For example, under warm, dry conditions, tire sanitizers may not be needed because simply driving the vehicle on the road may sufficiently reduce bacterial contamination.

However, in moist and cool conditions, sanitizers help reduce contamination. Again, the selection of the appropriate disinfectant is important (see Lesson #9).

Lesson #11

Animal carcasses for incineration, composting material or the dead pig pile are often visited by buzzards, rats, possums, raccoons and other scavenging wildlife. For this reason, mortality disposal should be considered one of the greatest risks to herd health, and disposal units should be operated to discourage vermin visits.

Lesson #12

Footbaths filled with disinfectants are a poor substitute for a brush and water hose if sanitation is truly the goal. With good intentions, many farms place footbaths filled with disinfectant at the entrance to buildings in hopes of preventing the spread of infectious agents between groups.

However, too often this effort fails to achieve the desired result. As Table 1 demonstrates, there is no substitute for removing organic matter to reduce contamination. Once a manure-laden boot enters the footbath, its beneficial contribution is negated.

Most of this article has focused on disease prevention. But it's also crucial to address the other part of the health equation, disease resistance.

Lesson #13

Vaccines are an adjunct to disease control, but to be effective, proper timing and administration are required. Too often, vaccination protocols are built around worker schedules rather than what is appropriate for optimization of pig immunity.

As a case in point, in most situations vaccination of pigs for erysipelas should occur between 8 and 10 weeks of age to avoid maternal immunity interference. However, many nursery operators will begin administration much earlier to spread out the workload. The result may be partial immunity, at best.

Vaccination timing is no longer a cookbook item. It requires full knowledge of disease and immune dynamics within the target population. This requires mapping of disease for serologic conversion and disease occurrence. Using this information, swine veterinary consultants can strategically overlay their understanding of passive immunity duration, risk of disease occurrence, and duration of vaccine protection to optimize vaccine efficacy. Again, this is herd- or system-dependent and cannot be generalized across farms.

Lesson #14

Medication should never be thought of as a substitute for good biosecurity. The pork industry is being closely scrutinized because it is a major user of antimicrobials. Consequently, the Food and Drug Administration has recently changed its regulations governing the animal drug approval process (Guidance Document 152). This new process suggests there will be greater restriction on antimicrobial use by producers and veterinarians.

To protect the pork industry's access to antimicrobials for the prevention, control and treatment of disease, it is imperative that the industry decrease its reliance on drugs and focus more on prevention through good management and disease exclusion. Producers and veterinarians need to justify every antimicrobial use on farms.

Lesson #15

Good husbandry covers a lot of biosecurity errors, but not all. Even the best producers with the best facilities cannot overcome the devastation that disease can cause.

Going forward, the swine industry needs to reexamine the role of health for its effect on the well-being of animals as well as health's contribution to the bottom line.

While animal activists are currently focusing on facility design as the major factor driving animal welfare, producers and veterinarians know that daily care and disease have a much greater impact. Not only does disease affect animal well-being, it can also be the difference between economic survival and demise.

Quality production, cheap feed and market access are still the kingpins driving profitability; however, disease remains a key determinant of farm survival, particularly in this new era of tight profit margins.

Lastly, train new employees to ensure that they understand the whys and wherefores of biosecurity programs so they can be properly carried out. Compliance is crucial.